There are many different types of earth retaining walls. Gravity walls, concrete walls, concrete and timber crib walls, and bin walls are just a few examples. All of these earth retaining walls undergo some deterioration over time. Additionally, there are numerous other reasons for repairing, replacing, or modifying retaining walls. The present invention is directed to replacement walls that can be used with any existing wall. Because bin walls are particularly prone to deterioration, the details of the present invention are illustrated using bin walls.
Steel bin walls are one type of earth retaining wall. Bin walls are constructed by erecting a system of adjoining boxes using lightweight steel members and backfilling the boxes with soil to form a gravity-type retaining wall. Over time, the steel members of the bin walls often corrode thereby weakening the wall. When the corrosion becomes severe, the wall must be repaired or replaced. Sometimes, due to other factors, an otherwise structurally sound wall must be strengthened.
Currently, repair or replacement of existing earth retaining walls such as bin type walls, use a number of common construction methods and structures. These methods include installing soldier piles and wood lagging behind or through the existing bin wall. All or a portion of the existing bin wall is thereafter removed as excavation proceeds. The bin wall is either replaced with a new bin wall or a different type of retaining wall is constructed in its place. The walls typically used to replace a bin wall include permanent tiedback walls and conventional cantilevered concrete retaining walls.
FIG. 1 illustrates tieback details of a conventional tiedback wall that is used as a replacement wall. As shown in the figure, tieback 1 is secured to soldier beam 2 through its outer anchorage 3 and pipe sleeve 7. The tensile member of tieback 1 is shown as a bar tendon and the soldier beam as an H-beam having flanges 2a. Pipe sleeve 7 passes through an opening in outer flange 2a and is secured to the web of beam 2 and bears on the inner flange 2a. Anchorage 3, including bearing plate 3a and nut 3b, fastens tieback 1 to soldier beam 2 and is encased within concrete wall 4. A tubular sleeve 5, including seal 5a, is disposed around tieback 1 through soldier beam 2. The sleeve and seal hold a corrosion inhibiting compound around the exposed end of the bar tendon. Other conventional structural elements include shear studs 6 attached to soldier beam 2, lagging boards 8, and drainage board 8a.
Two types of in-situ ground reinforcement devices used to support retaining walls are tiebacks and soil nails. Tiebacks, also referred to as ground anchors, are often used in the construction industry to support or anchor various structures in the ground. For example, they are often used to support retaining walls bordering highways or to support excavation sheeting to prevent cave-ins which would otherwise endanger lives and property. Such tiebacks generally include an elongate tensile member having an inner anchorage, an unbonded length, and an outer anchorage. The tensile member is often prestressing steel. Formed around the inner end of the tensile member is a cementitious grouted inner anchorage which anchors the tensile member to the earth and distributes to the surrounding ground tensile forces applied to the tensile member. The unbonded length separates the inner anchorage from the outer anchorage and allows the inner anchorage to be located deep behind the wall. The outer anchorage secures the outer end of the tensile member to an excavation sheeting system or other structure to be supported. An example of a typical tieback is illustrated in U.S. Pat. No. 3,490,242. Tiebacks are high load-carrying capacity reinforcement. Tiebacks are tested and tensioned by preloading during installation.
Soil nails, a type of in-situ ground reinforcement device, like tiebacks, provide support for retaining walls. More particularly, soil nails are untensioned tensile members that reinforce the retained earth. Soil nails extend from the retaining wall into the earth and are anchored to the earth along their entire length. They have a lower load-carrying capacity than tiebacks, do not extend as far into the earth as tiebacks, and, during installation, only a small percentage are tested. Soil nails assist in resisting earth pressures, support the weight of the earth, and prevent the formation of slip planes.
Known methods of replacing a deteriorating bin wall require disruption of the area and traffic behind the existing wall during installation of the replacement wall, and partial or complete demolition of the existing wall. There are three primary methods. One method requires the use of temporary sheeting to retain the earth during construction and structural backfill between the replacement wall and temporary sheeting. A second method is illustrated in FIG. 1 and requires that soldier beams be installed in or behind the existing wall.
In a third prior technique, bin walls are replaced by casting a reinforced concrete panel onto the face of the existing bin wall and then installing tiebacks through sleeves placed in the concrete. The tiebacks are locked off or fastened against the concrete panel. The tieback connection or outer anchorage which is exposed and protrudes from the concrete facing is covered with a cap. Because the tiebacks are installed through preexisting sleeves placed in the concrete facing, and the concrete facing is installed before the tiebacks are installed, the location of the tiebacks is fixed by the sleeves. Thus, it is very expensive and aesthetically undesirable to relocate the tiebacks when obstructions prevent the installation of the tiebacks at the location established by the sleeves, or when additional tiebacks are required to replace tiebacks which fail to carry the design load. Furthermore, the repaired wall has an outer anchorage that projects outside the finished wall unless the wall thickness is increased by approximately 8 inches to encase the outer anchorage. Projecting anchorage caps are unattractive and may encroach upon specified clearances which are intended to prevent accidents. Thus, projecting anchorhead caps may be a safety hazard to traffic. A wall of increased thickness suffers from this same problem. When the wall being repaired is along an established railroad or highway right-of-way, it is important to repair the wall using as little space as possible to avoid having to realign the right-of-way in order to maintain the specified clearance.